The US Department of Energy (DOE) Fuel Cell Technologies Office’ (FCTO) 2014 Hydrogen and Fuel Cells Program Annual Progress Report (earlier post)—an annual summary of results from projects funded by DOE’s Hydrogen and Fuel Cells Program—described a number of advances in the field of hydrogen storage.
The DOE Hydrogen Storage sub-program has developed a dual strategy. For the near-term, the focus is on improving performance and lowering the cost of high-pressure compressed hydrogen storage systems. For the long-term, the effort is on developing advanced cold/cryo-compressed and materials-based hydrogen storage system technologies.
The objective is to develop technologies that provide sufficient onboard hydrogen storage to allow fuel cell devices to provide the performance and run-time demanded by the application. For light-duty vehicles this means providing a driving range of more than 300 miles (500 km), while meeting packaging, cost, safety, and performance requirements to be competitive with current vehicles.
While some fuel cell electric vehicles (FCEVs) already have been demonstrated to travel more than 300 miles on a single fill using high-pressure tanks, DOE wants this driving range to be achievable across the full range of vehicle models without compromising space, performance, or cost.
By 2020, the sub-program has the following targets for automotive hydrogen systems:
- 1.8 kWh/kg system (5.5 wt%)
- 1.3 kWh/L system (0.040 kg H2/L)
- $10/kWh ($333/kg H2 stored)
Related to this, DOE seeks by 2020 to develop novel precursors and conversion processes capable of reducing the high-volume cost of high-strength carbon fiber by 25% from $13 per pound to ~$9 per pound.
To achieve the ultimate wide-spread commercialization of hydrogen FCEVs across the full range of light-duty vehicle platforms, the sub-program has established the following onboard hydrogen storage targets to meet the needs for full-fleet adoption:
- 2.5 kWh/kg system (7.5 wt%)
- 2.3 kWh/L system (0.070 kg H2/L)
- $8/kWh ($266/kg H2 stored)
Reducing the cost of high-pressure compressed hydrogen. Lightweight compressed gas storage vessels requiring a composite overwrap to contain hydrogen gas are considered the most likely near-term hydrogen storage solution for the initial commercialization of FCEVs, as well as for other early market applications. In 2013, Strategic Analysis Inc., working with Argonne National Laboratory (ANL) and the National Renewable Energy Laboratory (NREL) completed a thorough cost analysis for baseline Type IV 350- and 700-bar compressed hydrogen storage systems, for both single- and multi-tank configurations.
While the cost for the carbon fiber composite must be reduced to meet the ultimate cost targets, at lower manufacturing volumes, the cost of the balance-of-plant (BOP) components was shown to be the largest cost contributor. The piping/fittings, integrated in-tank valve, and pressure regulator were found to be the largest three cost contributors. These results will be used to develop strategies to reduce BOP costs.
|Projected costs, in 2013$, for BOP components for 700-bar compressed hydrogen storage systems produced at 500,000 systems per year. Source: DOE. Click to enlarge.|
In FY 2014, one area of focus was low-cost, high-strength carbon fiber precursors and advanced tank designs. Carbon fiber composite overwraps can currently contribute as much as 75% or more to the overall cost of advanced Type IV tanks. The Hydrogen Storage sub-program supported efforts at the Oak Ridge National Laboratory (ORNL) to reduce the cost of polyacrylonitrile (PAN)-based fibers used as precursors to produce high-strength carbon fibers. ORNL efforts focused on advanced precursor materials and processing since precursors have been shown to contribute over 50% of the total cost of high-strength carbon fibers.
The ORNL team investigated the use of low-cost textile-grade fibers made from PAN blended with a methyl acrylate comonomer (PAN-MA) as lower-cost precursors and continued to improve on the development of melt-spinnable PAN precursors and processing techniques to replace the current more costly wet processing methods.
The ORNL team reported increased tensile strength from 405 KSI to 649 KSI and tensile modulus from 33 MSI to 38 MSI for carbon fibers produced from PAN-MA precursor fibers manufactured on high-volume textile lines.
A team led by the Pacific Northwest National Laboratory (PNNL) focused on reducing the cost of a Type IV tank system by developing novel alternative resins and resin matrix modification, modifying the carbon fiber surface to improve composite translational efficiency, developing methods for alternative fiber placement and enhanced operating conditions that demonstrated routes to increase carbon fiber usage efficiency.
The PNNL team projected a 52% mass reduction and 30% cost reduction in compressed hydrogen storage systems with 5.6 kg hydrogen usable capacity, at 500 bar and cold (approximately 200 K) operating conditions, compared to baseline 700-bar ambient systems.
One new Small Business Innovation Research Phase II award was made that focuses on a graded construction approach of using a lower-cost, lower-performance carbon fiber in the outer layers where fibers are exposed to lower stress due to the thick wall effect with 700-bar Type IV tanks.
The program also made three new awards:
Materia Inc. will investigate use of a low-viscosity resin and a vacuum-assisted resin transfer molding process as alternatives to the traditional epoxy resin and wet-wind manufacturing process for Type IV tanks.
PPG Industries Inc. will investigate the production scale-up of an ultra-high-strength glass fiber (≥5,500 MPa) and evaluate its performance in composites and a low-cost alternative to carbon fiber in Type III and IV tanks.
Sandia National Laboratories (SNL) will screen alternative metal alloys for use in place of 316/316L stainless steel for materials of construction in balance of plant and other hydrogen applications, leading to lower costs and lower mass.
FY 2014 analysis also projected a 52% mass reduction and 30% cost reduction in compressed hydrogen storage systems with 5.6 kg hydrogen usable capacity, at 500 bar and ~200 K, operating conditions, compared to baseline 700-bar ambient systems.
Advanced materials. The advanced materials initiatives span a range of hydrogen storage technologies:
For metal hydrides, efforts emphasized material discovery coupled with reducing desorption temperatures and improving kinetics.
For chemical hydrogen storage materials, much of the focus was on developing reversible or regenerable liquid-phase materials, and also increasing efficiency of regeneration routes for solid-phase materials.
For hydrogen sorbents, efforts were focused on increasing the isosteric heat of adsorption, mainly through inclusion of open metal centers or boron doping, to increase the adsorbed capacity at higher temperatures and improving standard measurement practices for hydrogen capacity.
Also in FY 2014, the Hydrogen Storage sub-program maintained efforts to collect and disseminate materials data on advanced hydrogen storage materials through the hydrogen storage materials database.
The program made three new awards in FY 2014:
HRL Laboratories, with partners SNL and University of Missouri-St. Louis, is investigating two material systems, mixed metal borohydrides and lithiated boranes, with potential to offer high gravimetric capacity with fast kinetics at temperatures and pressures relevant to automotive applications.
Lawrence Livermore National Laboratory (LLNL), with partners SNL, Georgia Tech, and University of Michigan, will use a combined multi-scale computational and experimental approach to develop and validate strategies to improve the performance of Mg(BH4)2, a material with potential for 14 wt% reversible hydrogen storage.
Ardica Technologies, with partner SRI, will transition and scale up a version of the Savannah River National Laboratory (SRNL)-developed electrochemical method of alane (AlH3) production/regeneration from the laboratory to production to significantly lower the cost of alane compared to conventional solution synthesis methods.
Specific accomplishments for the year include:
Hydrogen desorption and decomposition pathways were studied for 2 LiBH4 + 5 Mg(BH4)2 using nuclear magnetic resonance; experimentally observed reaction products were consistent with theoretically predicted B2H6 anion. Using a combination of experiments and density functional theory, all but one reaction product was able to be assigned. (Northwestern University)
Developed the M2(4,6- dioxido benzene 1,3-dicarboxylate) (known as m-dobdc) (M = Mg, Mn, Fe, Co, Ni) series of metal organic frameworks via a new structural isomer that shows a significantly improved hydrogen binding enthalpy as compared to the regular M2(dobdc) for the Mn, Fe, Co, and Ni analogues. The open metal coordination sites are shown to have a greater positive charge in M2(m-dobdc) than in M2(dobdc), leading to the experimentally determined higher isosteric heats of H2 adsorption (~1.0 kJ/mol higher on average) and up to 40% increase in adsorption enthalpy. (Lawrence Berkeley National Laboratory, LBNL)
Demonstrated a volumetric capacity for Ni2(m-dobdc) at room temperature and 100 bar of 12.1 g/L, which is the highest demonstrated to date and 50% greater than H2 gas. (LBNL)
Developed recommended volumetric capacity definitions and measurement protocols to help the research community better report and understand their volumetric capacity material results. (NREL)
Hydrogen Storage Engineering Center of Excellence (HSECoE). In FY 2014, the HSECoE developed prototype designs and evaluation plans for each of the hexcell and MATI sorbent systems using a 2-L Type I (all metal) aluminum pressure vessel.
Of particular note, said Dr. Sunita Satyapal, Director, FCTO, the FCTO-supported engineering efforts delivered more than 9 kg of MOF-5 to HSECoE partners for Phase III testing, with scaled-up batch material achieving performance within 10% of lab-scale batch material, and demonstrated 20x improvement in MOF-5 thermal conductivity using an enhanced natural graphite layering approach compared to random loading.
The Hydrogen Storage sub-program also established the HSECoE model website page and posted the metal hydride (MH) acceptability envelope, MH finite element model, hydrogen tank mass and cost estimator, and hydrogen vehicle simulation framework models for public availability.